Method for calculating optimum gel concentration and dilution ratio for fracturing applications

Abstract

A method of preparing a fracturing slurry comprising a concentrated gel and water, the method comprising preparing a concentrated gel from a polymer and water, diluting the concentrated gel with additional water to form a fracturing carrier fluid at a predefined downhole concentration, preparing a fracturing slurry comprising the fracturing carrier fluid, and pumping the fracturing slurry downhole at or below a predefined maximum slurry rate. The fracturing carrier fluid is formed upon allowing the concentrated gel sufficient residence time to at least partially hydrate.

What is claimed: 
     
       1. A method of preparing a fracturing slurry comprising a concentrated gel and water, the method comprising:
 preparing a concentrated gel from a polymer and water in a hydration tank; 
 allowing the concentrated gel sufficient residence time to at least partially hydrate in the hydration tank; 
 delivering the concentrated gel to a mixing tee junction to which a water supply line is connected; 
 diluting the concentrated gel with additional water at the mixing tee junction to form a fracturing carrier fluid at a predefined downhole concentration; 
 delivering the fracturing carrier fluid to a header tank configured with a first-in-first-out flow configuration; 
 preparing a fracturing slurry comprising the fracturing carrier fluid; and 
 pumping the fracturing slurry downhole at or below a predefined maximum slurry rate. 
 
     
     
       2. The method of  claim 1 , further comprising: controlling a concentration of the concentrated gel based on the predefined downhole concentration and the predefined maximum slurry rate. 
     
     
       3. The method of  claim 1 , wherein the residence time of the concentrated gel is dependent on a concentration of the concentrated gel and a maximum concentrated gel rate. 
     
     
       4. The method of  claim 3 , wherein the residence time of the concentrated gel is sufficient to fully hydrate the concentrated gel. 
     
     
       5. The method of  claim 3 , wherein the residence time of the concentrated gel is sufficient to hydrate the gel at least 85%. 
     
     
       6. The method of  claim 3 , further comprising: controlling the maximum concentrated gel rate and a maximum dilution rate of the concentrated gel for the diluting. 
     
     
       7. The method of  claim 6 , further comprising determining, with the control system, a performance curve based on the maximum slurry rate and the downhole concentration and wherein controlling the maximum concentrated gel rate and the maximum dilution rate of the concentrated gel is based on at least on the performance curve. 
     
     
       8. The method of  claim 3 , wherein the maximum concentrated gel rate ranges from 0 bpm to 27 bpm. 
     
     
       9. The method of  claim 1 , further comprising: determining, with the control system, a hydration line based on a concentrated gel rate and on the concentration of the concentrated gel. 
     
     
       10. The method of  claim 9 , wherein an intersection of the hydration line with at least one performance curve defines the optimum concentration of the concentrated gel and the maximum concentrated gel rate. 
     
     
       11. The method of  claim 10 , further comprising: determining an actual gel rate setpoint based on the maximum concentrated gel rate and an actual slurry rate relative to the predefined maximum slurry rate. 
     
     
       12. The method of  claim 10 , further comprising: determining an actual dilution water rate setpoint based on a maximum dilution rate and an actual slurry rate relative to the predefined maximum slurry rate. 
     
     
       13. The method of  claim 1 , wherein a rate of delivering the concentrated gel and a rate of diluting the concentrated gel with water increase and decrease together to maintain a ratio to achieve the predefined downhole concentration in order to maintain a fluid level within the header tank. 
     
     
       14. A fracturing system used to prepare a fracturing slurry comprising a concentrated gel and water, the system comprising:
 a water supply line; 
 a polymer supply unit; 
 a mixer that blends the polymer supplied by the polymer supply unit and the water supplied by the water supply line to form a concentrated gel; 
 at least one hydration tank fluidly connected to the mixer to receive the concentrated gel; 
 a header tank that receives the fracturing carrier fluid from a tee junction, the tee junction fluidly connected to the at least one hydration tank and the water supply line, wherein the header tank is configured with a first-in-first-out configuration; 
 a control system configured, upon the concentrated gel reaching a predefined hydration level in the at least one hydration tank, to move the concentrated gel out of the at least one hydration tank and dilute the concentrated gel at the tee junction to form a fracturing carrier fluid and subsequently direct the fracturing carrier fluid to the header tank; 
 a mixer that blends the fracturing carrier fluid from the header tank with proppant supplied by a proppant supply tank to form a fracturing slurry; and 
 a pump for pumping the fracturing slurry downhole at or less than a maximum slurry rate. 
 
     
     
       15. The system of  claim 14 , wherein the control system is further configured to control a concentration of the concentrated gel based on a predefined downhole concentration and the maximum slurry rate. 
     
     
       16. The system of  claim 14 , wherein the header tank has a first-in first-out flow configuration which adds additional residence time to the diluted gel. 
     
     
       17. The system of  claim 14 , wherein a residence time of the concentrated gel in the at least one hydration tank is dependent on the concentration of the concentrated gel and on a maximum concentrated gel rate. 
     
     
       18. The system of  claim 17 , wherein the residence time of the concentrated gel in the at least one hydration tank is sufficient to fully hydrate the concentrated gel. 
     
     
       19. The system of  claim 17 , wherein the residence time of the concentrated gel in the at least one hydration tank is sufficient to hydrate the gel at least 85%. 
     
     
       20. The system of  claim 17 , wherein the control system is further configured to control the maximum concentrated gel rate and a maximum dilution rate of the concentrated gel as it is diluted in the header tank. 
     
     
       21. The system of  claim 20 , wherein the control of the maximum concentrated gel rate and the maximum dilution rate of the concentrated gel is based on at least a performance curve generated by the control system. 
     
     
       22. The system of  claim 17 , wherein the maximum concentrated gel rate ranges from 0 bpm to 27 bpm. 
     
     
       23. The system of  claim 14 , wherein the control system is further configured to increase and decrease a rate of delivering the concentrated gel and a rate of diluting the concentrated gel with water to maintain a fluid level within the header tank.